Changes in the global heat transport and eddy-mean flow interaction associated with weaker thermohaline circulation

Abstract

This study investigates the anomalous patterns of the oceanic and atmospheric heat transport, transient waves and the interaction between transient waves and the mean zonal flow. The evaluation is based on simulations performed with a coupled model forced by an increase of 1 Sverdrup of freshwater flux into the North Atlantic Ocean. It is found that an increase of freshwater flux in the North Atlantic leads to a weakening in the Northern Hemisphere (NH) oceanic heat transport by up to 1 Petawatt (1015) PW but results in an intensification of the Southern Hemisphere (SH) total heat transport. This inter-hemispheric seesaw leads to substantial changes in transient wave activity which is associated with anomalous meridional temperature flux and eddy kinetic energy (EKE). During winter in the NH, weakening of the thermohaline circulation induces an increase in the storm track activity. However, a reduction in storm tracks is found over the extratropical regions of the SH. The correspondence between the anomalies of storm track intensity and Eady growth rate lead to the conclusion that changes in the transient eddy activity are mostly generated by changes in baroclinic conditions. Furthermore, calculations of the E vector show that interaction between transient and mean flow is most pronounced over the North Atlantic where stronger storm tracks enhance the mean westerlies, thus minimising the effect of changes in the oceanic heat transport. Copyright © 2011 Royal Meteorological Society